In specific areas of industrialized nations, the rising incidence of hypospadias and cryptorchidism from 1950- 2000 parallels the production and use of some phthalates, anti-androgenic synthetic chemicals used as plasticizers, that have been found in the urine of over 90% of the general population in the United States. Genetic and environmental factors play a role in the development of abnormal development of male reproductive outcomes. Polymorphisms in several genes including AR, SRD5A2, INSL3/LGR8, ESR1, ESR2, ATF3, CTGF, and CYR61 are associated with adverse male reproductive development. Prenatal exposure to phthalates leads to hypospadias, cryptorchidism, and shortened anogenital distance (AGD) and smaller penile width (PW) in animal studies. Our hypothesis is that single nucleotide and repeat polymorphisms in genes involved in hormone mediated male genital development are associated with shortened AGD and ano-scrotal distance (ASD: a similar measure to AGD in animals) and smaller PW; and this relationship is modified by prenatal phthalate exposure. To address this hypothesis, the proposed GEAR (Genetics and the Environment Associated with Male Reproduction) study will genotype candidate genes and repeat polymorphism length in 400 male infants recruited into a prospective NIEHS-funded cohort study, TIDES (The Infant Development and Environment Study), and in whom AGD, ASD, and PW and maternal pregnancy urinary phthalate concentrations are being measured. We will obtain and genotype buccal swab/FTA card DNA samples from infants during already scheduled birth exams in TIDES. We will first examine the association between genetic variation in AR, ESR1, ESR2, SRD5A2, ATF3, INSL3/LGR8, CTGF, CYR61 and shortened AGD and ASD, and smaller PW; then proceed to test whether this association is modified by first trimester urine phthalate exposures. By taking advantage of a prospective parent study design, GEAR is cost effective and novel by allowing for assessment of genetic variation and phthalate exposures in male reproductive development. If a relationship exists between genetic polymorphisms associated with male reproductive abnormalities, phthalate exposure, and novel clinical phenotypes AGD, ASD, and PW, these findings would: 1) enhance understanding of the relationship between genotype and novel clinical phenotypes of early male genital development, and 2) be among the first studies to examine gene/phthalate interactions in male reproductive development, and 3) contribute to future research that uses genotype, environmental exposure, and phenotype to predict future male reproductive health.